It has been acknowledged that Borneo is one of the most important centres of plant diversity in the world. The flora of Borneo is conservatively estimated to harbour between 12,000 and 15,000 species of vascular plants, that is, about 5-6% of the world total. Of these, 40-50% are endemic to the island, and up to 80% of the endemic species in Borneo occur in Sabah and Sarawak.

The vascular plant flora of Sarawak comprises more than 8,000 species. Over 2,000 tree species have been enumerated whereas orchids would number more than 1000 species each, ferns account for 757 species and palms make up another 260 species. New species continue to be collected and recognized.

The complex soil and terrain, together with altitudinal sequence, give rise to a wide range of habitats for plants in Sarawak. Each of the forest types is distinctly different in morphological characteristics and species complexities. Floristically, the mixed dipterocarp forest and the old secondary forest are among the richest. Old secondary forests evolved from ex-shifting cultivation areas for more than 100 years and have been studied in Lanjak Entimau Wildlife Sanctuary.

The occurrence of understorey trees below 10 cm dbh and the non-tree flora are more variable among the forest types. An example from Lanjak Entimau Wildlife Sanctuary (LEWS), the largest sanctuary in Sarawak, is shown below.

Species Abundance and Density of Trees (>=10 cm dbh) Recorded from Different Forest Types in Lanjak Entimau Wildlife Sanctuary

Forest Type

Families

Genera

Species

Average No. of Trees/ha

Riparian

31

62

70

533

Alluvial

38

111

265

518

Old Secondary

53

144

376

588

Lowland Dipterocarp

52

152

494

810

Hill Dipterocarp

43

123

368

838

Summit Ridge

48

110

285

1,029

Submontane

40

73

123

968

Montane

33

55

93

1,106

In the 52 ha Long Term Ecological Plot (LTER) at Lambir National Park, 72 families, 278 genera and 1,083 species have been recorded. Number of trees per hectare for diameter class of 1-10 cm, greater than 10 cm and greater than 50 cm were 6269, 633 and 41 respectively.

Different families dominate the different forest types. A ranking is shown for 6 families in Lanjak Entimau Wildlife Sanctuary.

Ranking of Dominant Families in Different Forest Types in Lanjak Entimau Wildlife Sanctuary